Search results for "SUPERCONDUCTIVITY"
showing 10 items of 983 documents
The electron gas with a strong pairing interaction: Three particle correlations and the Thouless instability
2000
We derive simplified Faddeev type equations for the three particle T-matrix which are valid in the Hubbard model where only electrons with opposite spins interact. Using the approximation of dynamical mean field theory these equations are partially solved numerically for the attractive Hubbard model. It is shown that the three particle T-matrix contains a term vanishing $\sim T^2$ at the Thouless (or BCS) instability where the two-particle T-matrix diverges. Based on the three particle term we further derive the low density - strong coupling extension for the two-particle vertex function. We therefore understand our equations as a step towards a systematic low density expansion from the wea…
Microscopic quasiparticle–phonon description of beta decays of 113Cd and 115In using proton–neutron phonons
2007
Abstract The fourth-forbidden non-unique ground-state-to-ground-state beta decays of 113 Cd and 115 In are calculated using a realistic microscopic two-body interaction and a realistic single-particle model space. To describe the involved initial and final nuclear states we introduce a proton–neutron variant of the microscopic quasiparticle–phonon model (MQPM), the proton–neutron MQPM (pnMQPM). The states of the pnMQPM are created by coupling quasiparticles with phonons of the proton–neutron quasiparticle random-phase approximation (pnQRPA). The computed half-lives and log f t values are found to be in excellent agreement with experimental data. Computed beta spectra of the decays are also …
Quantum simulation of the spin-boson model with a microwave circuit
2017
We consider superconducting circuits for the purpose of simulating the spin-boson model. The spin-boson model consists of a single two-level system coupled to bosonic modes. In most cases, the model is considered in a limit where the bosonic modes are sufficiently dense to form a continuous spectral bath. A very well known case is the ohmic bath, where the density of states grows linearly with the frequency. In the limit of weak coupling or large temperature, this problem can be solved numerically. If the coupling is strong, the bosonic modes can become sufficiently excited to make a classical simulation impossible. Here, we discuss how a quantum simulation of this problem can be performed …
Crystal Fields in PrX3 (X=In, Tl, Pb, Sn) Intermetallic Compounds with Cu3Au Structure
1977
We have determined the crystal field splittings of Pr3+ in PrIn3, PrTl3, PrPb3, and PrSn3 by inelastic neutron scattering. The values of the deduced crystal field parameters are found to depend strongly on the constituent X, though all systems have nonmagnetic ground-states. The line widths in the different systems are compared.
On melting of two-dimensional monolayer films
1996
The melting of two-dimensional films formed on the (100) fcc crystal is studied by Monte Carlo simulation. The results obtained suggest that in systems with only weakly corrugated surface potential, exhibiting the hexagonal close packed solid structure, the melting transition is followed by the lsing-like transition as predicted by the theory of Nelson and Halperin. In the case of highly corrugated surface potential, the film forms registered structure which disorders gradually as the temperature is raised.
Nondiverging vortex pinning barriers at low current densities across the putative elastic vortex-glass–vortex-liquid transition inYBa2Cu3O7−δfilms
2001
A detailed analysis of the electric field--current density $(E\ensuremath{-}J)$ characteristics of ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ films across the putative thermally induced elastic vortex-glass--vortex-liquid transition predicted by the $E(J)$ curve scaling reveals that the expected increase of the collective pinning barriers with decreasing J is cut off in the low-$J$ region, signaling a dissipation process which involves the plastic deformation of the vortex system. The temperature and magnetic field dependence of the pinning barriers at low J does not change across the scaling-predicted glass transition line. For the investigated m…
Anomalous transport effects on switching currents of graphene-based Josephson junctions
2017
We explore the effect of noise on the ballistic graphene-based small Josephson junctions in the framework of the resistively and capacitively shunted model. We use the non-sinusoidal current-phase relation specific for graphene layers partially covered by superconducting electrodes. The noise induced escapes from the metastable states, when the external bias current is ramped, give the switching current distribution, i.e. the probability distribution of the passages to finite voltage from the superconducting state as a function of the bias current, that is the information more promptly available in the experiments. We consider a noise source that is a mixture of two different types of proce…
Switching times in long-overlap Josephson junctions subject to thermal fluctuations and non-Gaussian noise sources
2014
We investigate the superconducting lifetime of long current-biased Josephson junctions, in the presence of Gaussian and non-Gaussian noise sources. In particular, we analyze the dynamics of a Josephson junction as a function of the noise signal intensity, for different values of the parameters of the system and external driving currents. We find that the mean lifetime of the superconductive state is characterized by nonmonotonic behavior as a function of noise intensity, driving frequency and junction length. We observe that these nonmonotonic behaviours are connected with the dynamics of the junction phase string during the switching towards the resistive state. An important role is played…
Perpendicular transport properties of YBa_2Cu_3O_{7-\delta}/PrBa_2Cu_3O_{7-\delta} superlattices
2000
The coupling between the superconducting planes of YBa2Cu3O{7-\delta}/ PrBa2Cu3O{7-\delta} superlattices has been measured by c-axis transport. We show that only by changing the thickness of the superconducting YBa2Cu3O{7-\delta} layers, it is possible to switch between quasi-particle and Josephson tunneling. From our data we deduce a low temperature c-axis coherence length of 0.27 nm.
Time-dependent Landauer-B\"uttiker formalism for superconducting junctions at arbitrary temperatures
2015
We discuss an extension of our earlier work on the time-dependent Landauer--B\"uttiker formalism for noninteracting electronic transport. The formalism can without complication be extended to superconducting central regions since the Green's functions in the Nambu representation satisfy the same equations of motion which, in turn, leads to the same closed expression for the equal-time lesser Green's function, i.e., for the time-dependent reduced one-particle density matrix. We further write the finite-temperature frequency integrals in terms of known special functions thereby considerably speeding up the computation. Numerical simulations in simple normal metal -- superconductor -- normal m…